This invention relates to polymers which are useful as coatings. The reaction of isocyanates with organic compounds containing two or more active hydrogens such as polyamines and polyalcohols, to form polyureas and polyurethanes has been greatly studied in the prior art, and this general class of polymers has been found to possess many useful properties. Since isocyanates generally react quickly and efficiently with such compounds at room temperature, these two components usually must be mixed together only at the time and place at which reaction is desired. In an approach to making so-called "one-pot" formulations or compositions, in which the reacting materials are packaged together before using, and later activated, relatively unreactive derivates of isocyanates have been used which will regenerate the free isocyanate upon heating. Various catalysts are also often contained in these compositions to facilitate the regeneration of isocyanate. However, this heating process has several disadvantages when the isocyanate is to be used as a coating, since, for example, the size of the article to be coated or the nature of the material of the article may preclude heating to the temperature necessary for polymerization to occur. Thus, it would be extremely desirable to have polymer-forming compositions which are relatively stable on storage and which could be cured in the absence of any extensive heating and without the specific addition of other materials.
Bortnick, U.S. Pat. No. 2,718,516, is typical of the prior art teachings of the isocyanate polymerization reaction, and generally discusses the manufacture and polymerization of isocyanatoalkyl esters of acrylic acid. The polymerization taught by Bortnick requires the addition of organic compounds containing two or more active hydrogen atoms, such as polyamines, polyols, amino alcohols and polycarboxylic acids. Examples of these include ethylenediamine, diethylenetriamine, triethylenetetraamine, ethylene glycol, polyethylene glycols such as triethylene glycol, glycerol, penaerythritol, sorbitol, mannitol, oxalic acid, adipic acid, ethanolamine, diethanolamine and propanolamine. During cross-linking of the polymer, the polyols will be incorporated into the polymer cross-link structure. For example, ##STR1## In this reaction, the polyol has been completely incorporated into the polymer. The free end of the polyol will subsequently react with another isocyanato group, completing the cross-linkage.
The prior art, however, has never successfully developed a low cost, safe and easy-to-use curing system for isocyanato esters of acrylic acids. The methods previously known require on-site mixing of potentially hazardous chemicals (e.g., Bortnick) or the use of very expensive (and potentially hazardous) chemicals (e.g., U.S. Pat. No. 3,743,626, Emmons). Additionally, many methods require heating to complete the cure. Bortnick, for example, requires heating from 60.degree.-200.degree. C. With the increased cost of energy, a room temperature curable compound is very desirable.
Woo and Heinert ("Journal of Coatings Technology" 49, pages 82-86, September 1977) prepared polymers containing isocyanate and cured them with water. Their findings, however, were that the samples cured with water were equivalent to those cured with polyols. They were unable to identify any significant differences between the two systems.